Method of preventing aerial oxidation and color stain



Fatenteti Sept. it, 1945 iii STATS mm orrics METHODDF PREVENTING AERIAL OXIDA- TION AND COLOR STAIN Arnold Weissberger and Paul W. Vittum, Rochester, N. Y., assignors to Eastman Kodak Company. Rochester, N. Y.-, a corporation of New added directly to the emulsion layers or may bev incorporated in the developing solution, as described in Fischer U. S. Patent 1,102,028, granted June 30, 1914 or they may be incorporated in a water-permeable medium which is insoluble in the carrier for th silver halide, as described in Mannes & Godowsky U. S. Patent 2,304,940, granted December 15, 1942 and Jelley and Vittum U. S. Patent 2,322,027, granted June 15, 1943.

A difliculty frequently encountered in these processes is the formation of color fog or stain.

When the exposed material is developed in a color forming developer, dye fog is frequently formed in the emulsion layer. This is because the developing agent has been oxidized to some extent by the action of the air and the oxidized developer tends to couple with the color-forming compound at places in the photographic material where no silver image is produced. It is well known that in these processes the dye should be formed only where the silver halide is reduced to metallic silver thereby oxidizing the developing agent to a form which couples with the color former. Once the developing agent is oxidized, it couples immediately with the color former whether a photographic image is present or not. Aerial oxidation of the developer or oxidation by means other than the photographic image therefore converts the developer to a form which will immediately react with the color former to produce a color fog or stain. This effect is especially noticeable in'materials havamount of dye image produced and some of the compounds, when incorporated in the sensitive emulsion, tend to render the resulting dye image unstable to the action of light.

It is, therefore, an object of the present invention to provide a novel means of reducing or eliminating the formation of color fog in photographic emulsions. A further object is to provide a novel means for reducing or eliminating the aerial oxidation of photographic developers. A still further object is to provide stain inhibitors for incorporation in photographic developing solutions or prebaths used prior to color-formingdevelopment. Other objects will appear from thefollowing description of our invention.

These objects are accomplished by incorporating in the photographic developing solution or in a prebath used prior to color development, dihydroxy tartaric acid or dinitro tartaric acid or a salt, ester, or amide of these compounds.

. The compounds which we proposed to use have the following general formula:

where X is a hydroxyl group or a nitro group.

The salts of these compounds include the alkali metal salts such as the sodium salt.

Esters may be used such as the methyl or ethyl esters of dihydroxy tartaric acid or dinitro tartaric acid. Amide derivatives of these compounds include the reaction products of these acids with an amine such as aniline. The action of dihydroxy tartaric acid may be due to their ing couplers incorporated in the sensitive emulsion layersince there is no coupler in the developing solution to react with any developing agent which is oxidized by the action of the air. Fog or stain arisingxfrom these causes is not readily controlled by the same procedures used to control silver to; Methods for cont; olling color fog or stain have been described in Vittum and Wilder U. S. Patoxidation or color fog, cause a reduction in the reaction products with the aqueous alkaline solutions, e. g., tartronic acid.

We have found that the aerial oxidation ofboth black and white and color developers may be appreciably reduced by adding to the developing solution a dihydroxy tartaric acid or dinitro tartaric acid or. one of their salts, esters or amides.

When used in color forming developers, these compounds also appreciably reduce the Whatever the mechanism of the reaction, we have found it possible to reduce markedly the fog or stain density without seriously reducing the densities of the developed dye images.

The a ents used accordingtoour invention may also be incorporated in the sensitive emulsion itself, such as one or more of the emulsion layers of a multi-layer coating. The stain preventin agent may be distributed uniformly throughout the emulsion or where it is intended to be nondiffusing in the gelatin an ester of an aliphatic alcohol containing at least five carbon atoms is preferably used. When incorporated in the emulsion, the stain inhibitor may be incorporated in the gelatin itself or in the water-permeable, water-insoluble coupler containing media such as described in Mannes 8: Godowsky U. S. Patent 2,304,940 and Jelley and Vittum U. S. Patent 2,322,027.

The stain inhibitors may also be incorporated in nonsensitive layers of the photographic material such as filter layers, interlayers or overcoating layers.

Where the stain inhibitor is used in a prebath prior to color development, it should be of such low molecular weight that it diiiuses into the emulsion layer and it must be retained in the emulsion layer until color development begins. The photographic material should, accordingly, be bathed in a solution of the stain inhibitor just prior to the color development step. A similar result is obtained by incorporating the inhibitor in the color forming emulsion itself and stain prevention may, therefore, be accomplished by incorporating the inhibitor in a prebath just prior to color development or in the color developing solution itself.

The following compounds are suitable for use according to our invention:

OH 011 N02 HO-JJ-COOH HO-iP-COONa -HO -COOH HO- COOH HO- COONa HO COH When incorporated in a prebath or in a developing solution, these compounds are used in amounts ranging from about 1 gram to about 5 1 grams per liter of solution. More or less than these amounts may be employed but in general less than 1 gram produces very little result and the solubility limit is reached in the neighborhood of 5 grams per liter.

Our invention will be further illustrated by reference to the following specific examples:

Example 1 The following formula is a standard hydroquinone developer containing one of the inhibitors according to our invention:

The sodium'dihydroxytartrate was not compietely dissolved in these developers but the solution displayed improved properties with respect to aerial oxidation.

Example 2 The following example illustrates the incorporation of our compounds in a staining pyrogallol developer:

The following formula illustrates a color develope'r containing one of our inhibitors: 2-amino-5-diethylamino toluene HClLgram's Sodium sulfite (desiccated); Sodium carbonate (monohyd'rat Sodium metaborate Potassium bromide Dinitro tartaric acid Water to Our process is particularly withip materials where it is especially importantto reduce the minimum or fog densities:;- This applies both to negative developingpaper and'to-reversal paper as well as transparencyamaterialsv It Will be understood that the examplesand modifications disclosed hereingare' iillustrative only and that our invention is.toa.bestaken as limited only by the scope of the appended claims. 7

1. A photographic developing :solution having a reduced tendency toward-aerial=oxidation, 'com prising a photographic deveiopingi agent; and-a compound soluble in said developing olution'selected from the group consistlng ofii tartaric acid, dinitro tartaric acid esters and amides of saidacids' 2. A photographic developing-solutio 7 7 reduced tendency toward aerial oikidationcomprising a photographic developing gent and 1a compound having the following ge' ralfforrnula:

where X is selected from the class consisting of hydroxyl and ultra groups." c

3. A photographic developingisolution having a reduced tendency toward aerial oxidation comprising a photographic developing 4 agent and sodium dihydroxytartrate.

4. A photographic'developin'g solution having a reduced tendency toward aerial oxidation comprising a photographic developing *a'gent and dinitro tartaric acid.- r

5. The method of preventing the formation of coloring in a photographic silverqha'lide emulsion which is developed by a color forming development step, comprising subjecting said emulsion to the color forming development in the presence of a compound soluble in the developing solution selected from the group. consisting of dihydroxy to the color forming development in the presence of a compound having the general formula:

x ao-c-coon no- --COH g where X is selected from the class consisting of hydroxyl and nitrc groups.

7. The method of preventing the formation of color fog in a photographic silver halide emulsion which is developed-by a color forming development step, comprising subjecting said emulsion to the colon-forming development in the presence of sodium dihvdroxy tartrate.

8. The method of preventing the formation of color fog in a photographic silver halide emulsion which is developed by a color-forming development step, comprising subjecting said emulsion to the color forming development in the presence at dlnitro tartaric acid.

9. [i color-forming photographic paper developer capable of developing a colored image in the presence of a coupler compound, comprising a primary aromatic amino developing agent and a compound soluble in the developing solution selected from the group consisting of dlhydroxy tartaric acid, tro tartaric acid and the salts, esters and des of said acids.

10. A color-forming photographic developer capable of developing a colored image in the presence of a coupler compound, comprising a,

primary aromatic amino developing agent and sodium dihydroxy tartrate.

11. A color-forming photographic developer capable of developing a colored image in the presence of a coupler compound, comprising a primary aromatic amino developing agent and dinitro tartaric acid.

12. The method of preventing the formation of color fog in a silver halide emulsion which contains a non-diflusin-g coupler, comprisingbathing said emulsion after coating and just prior to a color-forming development step in a solution ota soluble compound selected from the group consisting of dihydroxy tartaric acid, dinltro tartaric acid and the salts, esters and. amides of said acids.

13. The method of preventing the formation of color fog in a silver halide emulsion which contains a non-difiuslng coupler, co prising bathing said emulsion after coating and st prior to a color-forming development step in a solution of sodium dihydroxy tartrate.

14. The method of preventing the formation of color fog in a silver halide emulsion which contains a non-diffusing coupler, comprising bathing said emulsion after coating and just prior to a color forming development step in a solu tion of dinitro tartaric acid. 

